Field of the Disclosure
This disclosure relates to a turbine volute for the turbocharger of an internal combustion engine. More particularly, this disclosure relates to a turbocharger housing having an asymmetrical twin scroll turbine volute combined with an integrated exhaust manifold cylinder head that may be designed to accommodate mixed, radial or axial flow turbines.
Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting the horsepower of the engine without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the exhaust manifold of the engine, a compressor housing connected to the intake manifold of the engine, and a center bearing housing disposed between and coupling the turbine and compressor housings together. The turbine housing defines a generally annular chamber, scroll or volute that surrounds the turbine wheel and that receives exhaust gas from the engine. The turbine assembly generally includes a nozzle that leads from the chamber into the turbine wheel. The turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing, connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines a line which is the axis of rotation. Exhaust gas flows from the chamber, scroll or volute through the nozzle to the turbine wheel and the turbine wheel is driven by the exhaust gas. The turbine thus extracts power from the exhaust gas and drives the compressor. The compressor receives ambient air through an inlet of the compressor housing and the air is compressed by the compressor wheel and is then discharged from the housing to the engine air intake. As the compressor impeller rotates, it increases the air density and air pressure delivered to the cylinders of the engine via the engine intake manifold.
The stream of exhaust gas discharged by a cylinder via the engine exhaust manifold involves a series of short bursts or pulses of exhaust gas. In engines with multiple cylinders, it is typical to group the cylinders in two cylinder groups or cylinder banks. The cylinders grouped in one cylinder bank exhaust into one exhaust gas discharge line and the cylinders grouped in the other cylinder bank exhaust into another separate exhaust gas discharge line. The two discharge lines then feed exhaust gas to the turbocharger such that the streams of exhaust gas provided by the two discharge lines are kept separate for as long as possible.
The amount of work that can be done across an exhaust turbine is determined by the pressure differential at the turbine inlet and turbine outlet. The greater the pre-turbine pressure (at the turbine inlet) compared to the post-turbine pressure (at the turbine outlet), the greater the amount of work that can be transmitted through the turbine/compressor shaft. At the turbine outlet is the exhaust. An engine exhaust is a system put in place to reduce emissions and noise through the use of as assortment of catalysts, filters, and mufflers. This assortment of components creates a restriction on the flow, causing an increased pressure at the turbine outlet relative to atmosphere. The turbine then creates an additional pressure differential, elevating turbine inlet pressure above that of the turbine outlet. The turbine uses this pressure differential to create turbine power. Although the turbine may recover this pressure differential and the additional wasted energy of the hot exhaust gas, the increased backpressure caused by the turbine can increase the pumping work of an engine, which will reduce fuel economy. It is desirable to minimize the pressure differential at the turbine inlet and outlet without hurting performance, and thereby reduce backpressure and reduce the pumping work of the engine. Additionally, if the pressure differential becomes large, the cylinder head exhaust port pressure can overcome the exhaust valve spring, causing unwanted hot exhaust gas to enter the cylinder via the exhaust valve prior to ignition, causing engine self-ignition and in some cases leading to premature failure.